Field of the Invention
The present invention relates to a sputtering target for use in forming a compound film that mainly contains Cu and Ga and a method for producing the same.
Description of the Related Art
Conventionally, a Cu—Ga target has been used as a material essential for producing a solar cell in which a Cu—In—Ga—Se quaternary alloy film (so-called “CICS film”) is used as a light absorbing layer by a so-called selenization (Se) method. The selenization method is a method in which a Cu—Ga target is subject to sputtering of about 500 nm, a film stack subject to sputtering of about 500 nm consisting of the Cu—Ga target and an In film formed thereon is subject to heat treatment in an H2Se gas at a temperature of 500° C., and then Se is diffused into CuGaIn to thereby form a Cu—In—Ga—Se compound film (see Patent Document 1).
On the other hand, in order to improve the power generation efficiency of a light absorbing layer consisting of a Cu—In—Ga—Se quaternary alloy film, the addition of Na to the light absorbing layer is required. For example, Non-Patent Document 1 proposes the fact that Na content in a precursor film (Cu—In—Ga—Se quaternary alloy film) is typically about 0.1%.